1. Field of the Invention
The present invention provides a thiophene derivative. In particular, the present invention provides a thiophene derivative suitable for use as an organic light-emitting material or a conductive material.
2. Descriptions of the Related Art
Currently, light-emitting diodes (LEDs) are commonly used. For example, most traffic lights and large monitors use inorganic LEDs. As for the organic material-based LEDs, they can be manufactured into displays. Also, it has been predicted that organic LEDs will be the mainstream of medium-size or mini-size displays in the next generation due to their advantages such as self-luminous property, high response rate, low power consumption, large viewing angle, light weight, thin thickness, high brightness, full-color, and ability to display animated images.
Organic light-emitting diodes (OLEDs), first published by Kodak in the 1980s, are display elements that use the electroluminescence of an organic light-emitting material, i.e., a property that shows reversible color change to provide display effects when a voltage or current is applied. The OLED is mostly composed of a pair of electrodes and an organic light emitting layer, wherein the organic light emitting layer includes a light emitting material.
In 1990s, D. D. Bradley found another conjugated polymer with electroluminescence, i.e., poly(p-phenylene vinylene). The conjugated polymers have since been applied in LEDs. The conjugated polymers are polymers where the main chain thereof is composed of mutually connected double bonds and single bonds. Such polymers have special photoelectric properties, and have been the focal point of the development of organic semiconductor materials.
Compared to inorganic LEDs, the polymer LEDs can be prepared more easily. Among the numerous conjugated polymers, polythiophene and its derivatives are especially representative conjugated polymers. In addition to superior stability and thermal stability, polythiophene and its derivatives also have electrochromic properties, and thereby can be used as conductive materials or light emitting materials. The conductive/light emitting materials are widely used in the electro-optical field, e.g., as conductive materials required for thin film transistors (TFTs), capacitors, solar cells, or fuel cells, or as light emitting materials of OLEDs. In addition, they can be used in anti-statics, sealing applications etc.
In the electro-optical field, the “relative quantum yield” is usually a basis for judging the luminous efficiency of electro-optical materials. In other words, electro-optical materials with a higher relative quantum yield demonstrate better luminous efficiency, while electro-optical materials with a lower relative quantum yield demonstrate poor luminescent efficiency. The relative quantum yield is measured by using Coumadine having a quantum yield of 0.55 under 10−5 M sulfuric acid solution as a standard with UV-absorbing spectrum and fluorescence emission spectrum. The relative quantum yields can be obtained from the ratio of the integration values of the above two spectrums and the refractive index of the testing solution.
The sulfur element in the structure of the conductive polymers of polythiophene and its derivatives will lower the relative quantum yield, and thereby lower the application efficiency. In view of this, the inventor of the present invention conducted a lot of research and found that the relative quantum yield of polythiophene or its derivatives can be increased to improve the applicability by doping an aromatic ring or heterocyclic ring.
Thus, the present invention provides a thiophene derivative, which has a better relative quantum yield. Also, the conjugation length can be changed by changing the structure of the thiophene derivative to change the color of luminescence, and thereby, the thiophene derivative can be more widely used. The longer the conjugation length is, the longer the wavelength of the emitted light (i.e., red shift) and the smaller the band gap (E) will be. On the contrary, the shorter the conjugation length is, the shorter the wavelength of the emitted light (i.e., blue shift) and the greater the band gap will be. The band gap can be obtained by the formula E=hc/λ=1240/λ, wherein λ is the wavelength at the intersection point of X-axis (wavelength axis) and the absorption peak of the longest wavelength of the UV spectrum. The conjugation length of the thiophene derivative can be changed by designing its molecular structure to adjust the color of luminescence, and thus, the thiophene derivative can be more widely used. Moreover, the solubility of the thiophene derivative of the present invention is improved in the presence of an aromatic ring, and thus, is more convenient for use.